Dynamic trial implants

ABSTRACT

A trial implant system including a trial implant configured to be temporarily inserted into an intervertebral space defined by a superior vertebral body and an inferior vertebral body is disclosed. The trial implant may include a superior plate and an inferior plate coupled to the superior plate. The superior plate may have a first mating portion that defines a first articulating interface and the inferior plate may have a second mating portion that defines a second articulating interface. The second articulating interface may be configured to interact with the first articulating interface of the superior plate such that at least one of the superior plate and the inferior plate is capable of movement relative to the other. The first and second articulating interfaces may be primary or auxiliary articulating interfaces. For example, the first and second articulating interfaces may be corresponding curved surfaces or they may be corresponding engagement features.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/783,111, filed May 19, 2010 which claims the benefit under 35 U.S.C.§119(e) to U.S. Provisional Application No. 61/179,566, filed on May 19,2009, the entireties of each being expressly incorporated herein byreference thereto.

BACKGROUND

Currently, trial implants are inserted into an intervertebral space toaccurately gauge the desired size and shape of a permanentintervertebral implant that is to be inserted during a total discreplacement (TDR) surgery. Thus, a plurality of trial implants havingvarying size and/or shape characteristics are inserted into theintervertebral space until the appropriate size and shape has beendetermined. Once a trial insert achieves a proper fit, it is then andthe permanent implant is inserted having size and shape characteristicsthat match the properly fitted trial implant. The permanent implantremains installed in the intervertebral space after the surgery has beencompleted. Conventional trial implants are monobloc, or formed from asingle piece of material, and are similar in form to those utilizedduring an interbody fusion surgery.

SUMMARY

In accordance with one embodiment, a dynamic trial implant system isprovided that mimics the articulation of the permanent implant intendedto be implanted so as to provide a more accurate determination of thepreferred implant size and shape.

Such a trial implant system may include a trial implant that isconfigured to be temporarily inserted into an intervertebral spacedefined by a superior vertebral body and an inferior vertebral body. Thetrial implant may include a superior plate and an inferior plate coupledto the superior plate. The superior plate may have a first matingportion that defines a first articulating interface and the inferiorplate may have a second mating portion that defines a secondarticulating interface. The second articulating interface may beconfigured to interact with the first articulating interface of thesuperior plate such that at least one of the superior plate and theinferior plate is capable of movement relative to the other. The firstand second articulating interfaces may be primary or auxiliaryarticulating interfaces. For example, the first and second articulatinginterfaces may be corresponding curved surfaces or they may becorresponding engagement features.

The trial implant system may also include an inserter instrument. Theinserter instrument may include a shaft and a locking block that istranslatable along the shaft. The locking block may include a lockingmechanism that is configured to engage a locking mechanism defined bythe trial implant to thereby restrict movement of the superior plate ofthe trial implant relative to the inferior plate. When the lockingmechanism of the locking block is disengaged from the locking mechanismof the trial implant, the superior plate will be able to move relativeto the inferior plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofexample embodiments of the invention, will be better understood whenread in conjunction with the appended drawings. For the purposes ofillustrating the trial implant assembly of the present application,there is shown in the drawings example embodiments. It should beunderstood, however, that the application is not limited to the precisearrangements and instrumentalities shown. In the drawings:

FIG. 1 is a side perspective view of a pair of vertebral bodiesseparated by an intervertebral space;

FIG. 2A is a side perspective view of a trial implant system includingan inserter instrument having a handle, a shaft and a locking block, anda trial implant having a superior plate coupled to an inferior plate inaccordance with one embodiment;

FIG. 2B is a detailed perspective view of a distal portion of the trialimplant system shown in FIG. 2A;

FIG. 2C is a side perspective view of the trial implant system shown inFIG. 2A with the locking block of the inserter instrument removed forclarity;

FIG. 2D is a side perspective view of the trial implant system shown inFIG. 2A with the inserter instrument decoupled from the trial implant;

FIG. 3A is a top perspective view of the superior plate of the trialimplant shown in FIGS. 2A-2D;

FIG. 3B is a bottom perspective view of the superior plate shown in FIG.3A;

FIG. 4A is a top perspective view of the inferior plate of the trialimplant shown in FIG. 2A-2D;

FIG. 4B is a bottom perspective view of the inferior plate shown in FIG.4A;

FIG. 5A is a side perspective view of the trial implant system shown inFIG. 2D showing the superior plate decoupled from the inferior plate;

FIG. 5B is a side perspective view of the trial implant system shown inFIG. 5A with the locking block of the insert instrument translated alongthe shaft and engaging the superior plate to thereby restrict movementof the superior plate relative to the inferior plate;

FIG. 6A is a perspective view of the trial implant system shown in FIG.5B with the locking block removed;

FIG. 6B is a side elevation view of the trial implant system shown inFIG. 6A with the superior plate in a first moved position relative tothe inferior plate;

FIG. 6C is a side elevation view of the trial implant system shown inFIG. 6A with the superior plate in a second moved position relative tothe inferior plate;

FIG. 7A is a side elevation view of a trial implant system including aninserter instrument having a handle, a shaft and a locking block, and atrial implant having a superior plate coupled to an inferior plate inaccordance with another embodiment;

FIG. 7B is a detailed side view of the trial implant system shown inFIG. 7A with the handle of the inserter instrument removed for clarity;

FIG. 7C is a side view of the trial implant system shown in FIG. 7B withthe locking block of the inserter instrument removed for clarity;

FIG. 7D is a perspective view of the trial implant system shown in FIG.7A with the locking block disengaged from the superior plate;

FIG. 7E is a perspective view of the trial implant system shown in FIG.7D with the locking block engaging the superior plate to therebyrestrict movement of the superior plate relative to the inferior plate;

FIG. 8 is a perspective view of the trial implant system shown in FIG.7E with a distractor disposed about the trial implant;

FIG. 9A is a top perspective view of a trial implant system inaccordance with another embodiment, showing a superior plate decoupledfrom an inferior plate;

FIG. 9B is a bottom perspective view of the trial implant shown in FIG.9A;

FIG. 9C is a cut-away perspective view of the trial implant shown inFIG. 9A, with the superior plate coupled to the inferior plate;

FIG. 10A is a perspective view of a trial implant system including alocking block and the trial implant shown in FIGS. 9A-9C, in accordancewith another embodiment, with the locking block disengaged from thetrial implant;

FIG. 10B is another perspective view of the trial implant system shownin FIG. 10A;

FIG. 10C is another perspective view of the trial implant system shownin FIG. 10B, with the locking block engaging the trial implant;

FIG. 11A is an exploded perspective view of a trial implant systemincluding a trial implant having a superior plate and an inferior platein accordance with another embodiment;

FIG. 11B is a side elevation view of the trial implant shown in FIG. 11Awith the superior plate moved into a first position relative to theinferior plate;

FIG. 11C is a side view of the trial implant shown in FIG. 11A with thesuperior plate moved into a second position relative to the inferiorplate;

FIG. 11D is a cut-away perspective view of the trial implant shown inFIG. 11A;

FIG. 11E is a sectional side elevation view of the trial implant shownin FIG. 11C;

FIG. 11F is a sectional side elevation view of the trial implant shownin FIG. 11D;

FIG. 12A is a side elevation view of a trial implant system including ameasuring member in accordance with another embodiment;

FIG. 12B is an exploded assembly view of the trial implant system shownin FIG. 12A;

FIG. 13A is a side perspective view of a trial implant system includinga trial implant, an inserter instrument, and a pair of chisels inaccordance with another embodiment;

FIG. 13B is an exploded assembly view of the trial implant system shownin FIG. 13A; and

FIG. 13C is another exploded assembly view of the trial implant shown inFIG. 13A.

DETAILED DESCRIPTION

Referring to FIG. 1, a superior vertebral body 10 a defines a superiorvertebral surface 14 a of an intervertebral space 18, and an adjacentinferior vertebral body 10 b defines an inferior vertebral surface 14 bof the intervertebral space 18. Thus, the intervertebral space 18 isdisposed between the vertebral bodies 10 a-b. The vertebral bodies 10a-b can be anatomically adjacent vertebral bodies, or can remain after avertebral body has been removed from a location between the vertebralbodies 10 a-b. As illustrated, the intervertebral space 18 isillustrated after a discectomy, whereby the disc material has beenremoved or at least partially removed to prepare the intervertebralspace 18 to receive a disc implant that can achieve height restoration.Prior to inserting the permanent disc implant in the intevertebralspace, one or more temporary trial implants of various dimensions, suchas a movable/dynamic trial implant 22 of a trial implant system 26illustrated in FIGS. 2A-2D, are inserted into the intervertebral space18 to determine the optimal size and geometry of the actual disc implantto be permanently inserted. The implant 22 is configured such that asurgeon will be able to find the best permanent implant that matcheswith the intervertabral space 18 morphology. The intervertebral space 18can be disposed anywhere along the spine as desired, including at thelumbar, thoracic, and cervical regions of the spine.

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “lower” and “upper”designate directions in the drawings to which reference is made. Thewords “inner” or “distal” and “outer” or “proximal” refer to directionstoward and away from, respectively, the geometric center of the implantand related parts thereof. The words, “anterior”, “posterior”,“superior,” “inferior,” “medial,” “lateral,” and related words and/orphrases are used to designate various positions and orientations in thehuman body to which reference is made and are not meant to be limiting.The terminology includes the above-listed words, derivatives thereof andwords of similar import.

The trial implant system 26 is described herein as extendinghorizontally along a longitudinal direction “L” and lateral direction“A”, and vertically along a transverse direction “T”. Unless otherwisespecified herein, the terms “lateral,” “longitudinal,” and “transverse”are used to describe the orthogonal directional components of variouscomponents. It should be appreciated that while the longitudinal andlateral directions are illustrated as extending along a horizontalplane, and that the transverse direction is illustrated as extendingalong a vertical plane, the planes that encompass the various directionsmay differ during use. For instance, when the trial implant 22 isimplanted into an intervertebral space, such as the intervertebral space18, the transverse direction T extends vertically generally along thesuperior-inferior (or caudal-cranial) direction, while the horizontalplane defined by the longitudinal direction L and lateral direction Alies generally in the anatomical plane defined by the anterior-posteriordirection, and the medial-lateral direction. Accordingly, thedirectional terms “vertical” and “horizontal” are used to describe theimplant system 26 and its components as illustrated merely for thepurposes of clarity and illustration.

Referring now also to FIGS. 2A-2D, a trial implant system 26 isconfigured to be temporarily positioned within an at least partiallycleared out disc space, such as the disc space 18 disposed between thesuperior vertebral body 10 a and the inferior vertebral body 10 b. Thetrial implant system 26 includes a trial implant 22 coupled to aninserter instrument 30. The inserter instrument 30 can be formed fromany desired material such as stainless steel, while the trial implant 22can be formed from any desired material such as a titanium alloy. Itshould be appreciated that both the inserter instrument 30 and the trialimplant 22 can be formed from a range of biocompatible metals orpolymers, such as cobalt chromium molybdenum (CoCrMo), titanium andtitanium alloys, stainless steel, ceramics, or polymers such aspolyetheretherketone (PEEK), polyetherketoneketone (PEKK), andbioresorbable materials.

The inserter instrument 30 includes a shaft 34 having a shaft body 38that defines a proximal end 42 a, and a distal end 42 b that isseparated from the proximal end 42 a along a longitudinally extendingcentral shaft axis S. The shaft 34 includes a handle coupling portion 46at the proximal end 42 a of the shaft body 38, and a trial implantcoupling member 50 at the distal end 42 b of the shaft body 38. Thehandle coupling portion 46 may be a hex coupling configured to bereceived by a corresponding coupling portion of a handle, such as handle350 shown in FIG. 7A. As shown in FIG. 2D, the coupling member 50 isconfigured to be coupled to a complementary coupling member 54 of thetrial implant 22 so as to connect the shaft 34 and thus the inserterinstrument to the trial implant 24. In the illustrated embodiment, thecoupling member 50 of the inserter instrument 30 includes externalthreads (not shown for clarity) disposed proximate to the distal end ofthe shaft 34 configured to engage threads of the trial implant 22 tothereby couple the inserter instrument 30 to the trial implant.

When the inserter instrument 30 is coupled to the trial implant 22, theproximal end 42 a of the shaft body 38 defines a proximal end 62 a ofthe implant system 26, and the trial implant 22 defines an opposeddistal end 62 b of the implant system 26. Accordingly, a distal spatialrelationship is used herein to refer to a longitudinal direction for theproximal end 62 a toward the distal end 62 b, and a proximal spatialrelationship is used herein to refer to a longitudinal direction fromthe distal end 62 b toward the proximal end 62 a.

As shown in FIGS. 2A, 2B, and 2D, the inserter instrument 30 alsoincludes a locking block 68 having a tube 72 translatable about anexternal surface of the shaft body 38, and a head portion 76 extendingfrom a distal end of the tube 72. As shown, the tube 72 and the headportion 76 include a longitudinal bore 80 extending completelytherethrough, and the shaft body 38 extends through the bore 80. Thus,the locking block 68 is capable of translating distally and proximallyalong the shaft body 38. As best shown in FIG. 2D, the head portion 76includes a head body 82 and a locking mechanism 84 that extends distallyfrom the head body 82 toward the trial implant 22. In the illustratedembodiment, the locking mechanism 84 includes a pair of pins 88 thatextend toward the trial implant 22. As shown, the locking mechanism 84is configured to engage a complementary locking mechanism 92 of thetrial implant 22.

As shown in FIG. 2D, the trial implant 22 that is configured to becoupled to the distal end of the inserter instrument 30, includes anupper or superior plate 100, coupled to a lower or inferior plate 104.The superior plate 100 is coupled to the inferior plate 104 such thateither the superior plate 100, the inferior plate 104, or both iscapable of movement relative to the other. Such movement allows thetrial implant 22 to at least partially simulate actual implant movement,and thus provide an image of the final implant on implantation.Furthermore, it should be understood that the trial implant 22 may beprovided in a variety of dimensions depending on the individualreceiving the implant and the location of the intervertebral space thatreceives the trial implant.

As shown in FIGS. 3A-3B, the superior plate 100 of the trial implant 22,includes a generally oval shaped body 110 having a first mating portion114 incorporated into a bottom or inferior side of the body 110. Asshown, the body 110 defines an upper or superior, or outer transverseengagement surface 118 configured to contact the inferior endplate ofthe superior vertebral body 10 a, a curved proximal surface 122 and acurved distal surface 126. While the superior surface 118 is generallyflat, the superior surface 118 includes medial stabilizers 130, andlateral stabilizers 134 that serve to prevent the trial implant 22 fromslipping or becoming displaced within the disc space during andsubsequent to insertion. As shown, the medial stabilizers 130 aredisposed along the longitudinal direction and the lateral stabilizers134 are disposed along the lateral direction. Alternatively or inaddition thereto, teeth or other surface texturing can extend up fromthe superior surface 118 to prevent displacement of the trial implant22. The superior surface 118 further includes a pair of spaced apartrails or grooves 142 disposed along the longitudinal direction forreceiving upper arms of a distractor instrument, such as the upper armsof the distractor instrument 400 shown in FIG. 10.

As shown in FIGS. 3A-3B, the proximal surface 122 of the body 110defines a locking mechanism 92 of the trial implant 22 that isconfigured to engage the locking mechanism 84 defined by the inserterinstrument 30 to thereby restrict movement of the superior plate 100relative to the inferior plate 104. As shown, the locking mechanism 92includes two bores or holes 154 extending into the proximal surface 122of the superior plate 100. Thus, each pin 88 of the inserterinstrument's locking mechanism 84, is configured to be received by arespective bore 154 of the trial implant's locking mechanism 92.Furthermore, a partial bore 158 extends into the proximal surface 122 ofthe superior plate 100 between the bores 154. The partial bore 158provides clearance for the shaft 34 of the inserter instrument 30 whenthe inserter instrument is attached to the trial implant 22.

As shown in FIG. 3B, the first mating portion 114 defines a primaryarticulation interface such as an inferior articulating surface 160 andan auxiliary articulation interface such as an engagement feature 164for coupling the superior plate 100 to the inferior plate 104. Theinferior surface 160 is curved along the longitudinal direction and isconcave. Because the inferior surface 160 is concave, the first matingportion 114 also defines two opposing side surfaces 168. As shown inFIG. 3B, the engagement feature 164 is incorporated into the sidesurfaces 168. In particular, the engagement feature 164 includes a pin172 that extends laterally out from each respective side surface 168. Asshown, the pins 172 are located proximate to the longitudinal center ofeach side surface 168.

As shown in FIGS. 4A-4B, the inferior plate 104, includes a generallyoval shaped body 210 having a second mating portion 214 incorporatedinto a top or superior side of the body 210. As shown, the body 210defines a lower or inferior, or outer transverse engagement surface 218configured to contact the superior endplate of the inferior vertebralbody 10 b, a curved proximal surface 222 and a curved distal surface226. While the inferior surface 218 is generally flat, the inferiorsurface 218 includes medial stabilizers 230, and lateral stabilizers 234that serve to prevent the trial implant 22 from slipping or becomingdisplaced within the disc space during and subsequent to insertion. Asshown, the medial stabilizers 230 are disposed along the longitudinaldirection and the lateral stabilizers 234 are disposed along the lateraldirection. Alternatively or in addition thereto, teeth or other surfacetexturing can be included to prevent displacement of the trial implant22. The inferior surface 218 further includes a pair of spaced apartrails or grooves 242 disposed along the longitudinal direction forreceiving lower arms of a distractor instrument, such as the lower armsof the distractor instrument 400 (shown in FIG. 10).

As shown in FIGS. 4A-4B, the proximal surface 222 of the body 210defines the coupling member 54 of the trial implant 22 that isconfigured to couple the trial implant 22 to the inserter instrument 30.As shown, coupling member 54 includes a bore 246 that extendslongitudinally into the proximal surface 222 of the inferior plate 100.The bore 246 is sized to receive the external threads of the shaft 34.Thus, the bore 246 includes internal threads disposed about theperiphery of the bore 246 that are configured to mate with the externalthreads of the shaft 34 so as to couple the inserter instrument 30 tothe trial implant 22.

As shown in FIG. 4A, the second mating portion 214 defines a primaryarticulation interface, such as a superior articulating surface 260 andan auxiliary articulation interface, such as an engagement feature 264for coupling the inferior plate 104 to the superior plate 100. Thesuperior surface 260 is curved along the longitudinal direction and isconvex. Because the superior surface 260 is convex, the second matingportion 214 also defines two outer side surfaces 268. As shown in FIG.4B, the engagement feature 264 is defined in the side surfaces 268. Inparticular, the engagement feature 264 includes a slot 272 that extendslaterally into each respective side surface 268. Each slot 272 alsoextends in the longitudinal direction and follows an arch that issimilar to the arch of the curved superior surface 260. Proximate to theproximal end of each slot 272 is an opening 276 that extends downthrough the superior surface 260 and into a respective slot 272. Asshown, the slots 272 are located proximate to the longitudinal center ofeach side surface 268.

As shown in FIG. 5A, the inserter instrument 30 is coupled to the trialimplant 22 by threaded engagement of the threaded coupling member 50 ofthe inserter instrument shaft 34 with the threaded engagement member 54defined by the inferior plate 104 of the trial implant 22. As shown, thesuperior plate 100 may be coupled to the inferior plate 104, once theinserter instrument 30 is secured to the inferior plate 104. This isaccomplished by lowering the superior plate 100 onto the inferior plate104 such that the pins 172 of the superior plate 100 enter throughrespective openings 276 and into the slots 272 of the inferior plate104. Because of the engagement between the pins 172 and the slots 272the superior plate 100 will be able to move relative to the inferiorplate 104.

As shown in FIG. 5B, the movement of the superior plate 100 relative tothe inferior plate 104 may be restricted by advancing the locking block68 distally until the pins 88 of the locking block 68 engage the bores154 of the superior plate 100. Once the movement of the superior plate100 is restricted, the inserter instrument 30 may insert the trialimplant into the intervertebral space 18.

As shown in FIGS. 6A-6C, the locking block 68 may be translatedproximally until the pins 88 are completely removed from the bores 154of the superior plate 100. Once removed, the superior plate 100 will beable to move relative to the inferior plate 104. For example, thesuperior plate 100 may be moved to a first position as shown in FIG. 6Bin which the superior plate 100 is moved distally about the inferiorplate 104. In particular, the pin 172 of the superior plate 100 slidesdistally within the slot 272 of the inferior plate 104, while theinferior surface 160 of the superior plate 100 slides along the superiorsurface 260 of the inferior plate. The curved inferior and superiorsurfaces 160, 260, allow the superior plate 100 to move distally alongan arc in the longitudinal direction.

Similarly, the superior plate 100 may be moved to a second position asshown in FIG. 6C in which the superior plate 100 is moved proximallyabout the inferior plate 104. In particular, the pin 172 of the superiorplate 100 slides proximally within the slot 272 of the inferior plate104, while the inferior surface 160 of the superior plate 100 slidesalong the superior surface 260 of the inferior plate. The curvedinferior and superior surfaces 160, 260, allow the superior plate 100 tomove proximally along an arc in the longitudinal direction. As shown,because the curved inferior and superior surfaces 160, 260 are arcedonly in the longitudinal direction, movement of the superior plate isrestricted to the longitudinal direction.

As shown in FIGS. 7A-7E, the trial implant system 26 may include aninserter instrument constructed to include a stop member. As shown inFIGS. 7A-7C, an inserter instrument 330 includes a shaft 334 having ashaft body 338, a sleeve 342 translatable about the shaft body 338, anda locking block 346 coupled proximate to a distal end of the shaft body338. The instrument 330 also includes a stop member 346 attached to thelocking block 346. The inserter instrument 330 is configured to not onlyinsert the trial implant 22 but is also configured to measure the depthof the inserted trial implant 22.

As shown in FIGS. 7A-7C, the shaft body 338 is elongate in thelongitudinal direction and includes a distal end that is configured tocouple the inserter instrument 330 to the trial implant 22, and aproximal end that is configured to couple the inserter instrument 330 toa handle 350. Though not shown, the distal and proximal ends of theshaft body 338 may be similar to those described in reference to shaftbody 38. Therefore, the distal end of shaft body 338 may includeexternal threads and the proximal end of shaft body 338 may include ahex. As shown in FIG. 7C, the shaft body 338 further includes indiciamarks 354 near its proximal end. The indicia marks 354 providemeasurements for a user to determine the depth of the inserted trialimplant 22.

As shown in FIGS. 7A and 7B, the sleeve 342 is disposed about the shaftbody 338 such that the shaft body 338 is capable of translating withinthe sleeve 342. As shown, the sleeve 342 includes a pair of opposingslots 358 proximate to its distal end. The slots 358 extend laterallycompletely through the sleeve 342, and along the sleeve 342 in thelongitudinal direction.

As shown in FIGS. 7C, 7D and 7E, the locking block 346 is attached tothe shaft body 338 proximate to a distal end of the shaft body 338. Inparticular, the locking block 346 includes an arm 362 that extends outlaterally from the shaft body 338 and then distally in the longitudinaldirection. As shown, the arm 362 extends through the slot 358 defined bythe sleeve 342. Because the arm 362 extends through the slot 358, thelocking block 346 will be capable of moving with the shaft 330 relativeto the sleeve 342 as the shaft 330 is translated distally or proximally.Furthermore, the slot 358 will prevent the locking block 346 fromrotating as the shaft 330 is translated distally or proximally. This isbecause the transverse height of the arm 362 is substantially equal tothe transverse height of the slot 358.

As shown in FIG. 7D, the locking block 346 further includes a headportion 370 at the distal end of the arm 362. As shown, a stop member374 extends in the transverse direction from the head portion 370 and alocking mechanism 378 extends distally from a distal face of the headportion 370, as shown in FIG. 7D.

The locking mechanism 378 includes a pin 380 that is configured toengage a locking mechanism of the trial implant 22, such as a bore 381defined in the superior plate 100 of the trial implant 22. As shown inFIGS. 7D and 7E, the pin 380 is configured to engage the bore 381. Whenthe pin 380 is engaged with the bore 381 of the superior plate 100, asshown in FIG. 7E, the superior plate 100 is restricted from movingrelative to the inferior plate 104 and the trial implant 22 may beimplanted into the intervertebral space 18. Alternatively when the shaft334 is translated proximally, the pin 380 will disengage from the bore381, and the superior plate 100 will be able to move relative to theinferior plate 104.

As shown in FIG. 7D, the stop member 374 includes a first stop 382 thatextends up from a top surface of the head portion 370 and a second stop386 that extends down from a bottom surface of the head portion 370. Thestop member 374 and in particular the first stop 382 and second stop 386extend such that they have an overall height that is greater than theheight of the trial implant 22.

In operation, the inserter instrument 330 is coupled to the trialimplant 22, such that the pin 380 is engaged with the bore 381, thefirst stop 382 abuts or otherwise engages the superior plate 100, andthe second stop 386 abuts or otherwise engages the inferior plate 104.The trial implant 22 may then be inserted into the intervertebral space18. By rotating the handle 350 counter clockwise the shaft 330 willunscrew from the inferior plate 104 and move the first and second stops382, 386 proximally away from the trial implant 22. This will allow thetrial implant 22 to be inserted deeper into the intervertebral space 18.When the appropriate depth has been achieved, the locking block 346 ismoved distally, and reengages the trial implant 22. That is, the pin 380reengages the bore 381, the first stop 382 reengages the superior plate100, and the second stop 386 reengages the inferior plate 104. The depthof the trial implant 22 may then be measured using the indicia 354 onthe shaft body 338.

As shown in FIG. 8, the trial implant system 26 may also include adistractor instrument 400 for separating the superior and inferiorvertebras 10 a and 10 b. As shown, the distractor 400 includes an upperarm 404 that terminates distally in a pair of upper fork arms 408 a, 408b, and a lower arm 412 that terminates distally in a pair of lower forkarms 416 a, 416 b. The upper fork arms 408 a, 408 b are configured toslidingly engage the grooves 142 of the superior plate 100, and thelower fork arms 416 a, 416 b are configured to slidingly engage thegrooves 242 of the inferior plate 104, during the insertion of thecoupled superior and inferior plates 100, 104 into the cleared outintervertebral disc space 18. The distractor instrument 400 creates, viathe pivoting of the upper and inferior arms 404 and 412, and maintainsthe distraction of the cleared out space 18 while allowing the trialimplant 22 to be guided along the fork arms 408 a, 408 b, 416 a, and 416b.

The trial implant system 26 may include other trial implants includingother features to couple the superior plate to the inferior plate and torestrict movement of the superior plate relative to the inferior plate.For example, as shown in FIGS. 9A-9C, a trial implant 522 includes asuperior plate 526 coupled to an inferior plate 530, and is configuredto move relative to the inferior plate 530.

As shown in FIGS. 9A and 9B, the superior plate 526 includes a generallyoval shaped body 534 having a first mating portion 538 incorporated intoa bottom or inferior side of the body 534. As shown, the body 534defines an upper or superior, or outer transverse engagement surface 542configured to contact the inferior endplate of the superior vertebralbody 10 a, a proximal surface 546 and a distal surface 550. The superiorsurface 542 is generally flat and includes a pair of spaced apart railsor grooves 554 disposed along the longitudinal direction for receivingarms of a distractor instrument, such as the distractor instrument 400shown in FIG. 10.

As shown in FIGS. 9A and 9B, the proximal surface 546 of the body 534defines a locking mechanism 558 of the trial implant 522 that isconfigured to engage a locking mechanism defined by an inserterinstrument. As shown, the locking mechanism 558 includes an angledrecess 562 extending from a generally bottom portion of the proximalsurface 546 and through to the superior surface 542 of the superiorplate 100. As shown the recess 562 is defined by an angled bottomsurface 566 and opposing side surfaces 570. The recess is configured toreceive a locking mechanism defined by the inserter instrument.Furthermore, a partial bore 574 extends into the angled surface 566 ofthe superior plate 100 to provide clearance for a shaft, such as shaft34 of the inserter instrument 30 when the inserter instrument isattached to the trial implant 522.

As shown in FIG. 9B, the first mating portion 538 defines a primaryarticulation interface, such as an inferior articulating surface 580 andan auxiliary articulating interface, such as an engagement feature 584for coupling the superior plate 100 to the inferior plate 104. Theinferior surface 580 is curved along the longitudinal direction and isconcave. As shown in FIG. 9B, the engagement feature 584 extends downfrom the inferior surface 580 and defines a T-shaped protrusion 588. Inparticular, the engagement feature 584 includes a first member 592 thatextends down from the inferior surface 580 and a second member 596 thatextends in the lateral direction from an end of the first member 592. Asshown, the T-shaped protrusion 588 is disposed proximate to the centerof the inferior surface 580.

As shown in FIGS. 9A-9B, the inferior plate 530, includes a generallyoval shaped body 600 having a second mating portion 604 incorporatedinto a top or superior side of the body 600. As shown, the body 600defines a lower or inferior, or outer transverse engagement surface 608configured to contact the superior endplate of the inferior vertebralbody 10 b, a proximal surface 612 and a distal surface 616. The inferiorsurface 608 is generally flat and includes a pair of spaced apart railsor grooves 620 disposed along the longitudinal direction for receivinglower arms of a distractor instrument, such as the arms of thedistractor instrument 400 (shown in FIG. 10).

As shown in FIGS. 9A-9B, the proximal surface 612 of the body 600defines a coupling member 624 that is configured to couple the trialimplant 522 to an inserter instrument, such as the inserter instrument30. As shown, coupling member 624 includes a bore 628 that extendslongitudinally into the proximal surface 612 of the inferior plate 530.The bore 628 is sized to receive external threads of a shaft of aninserter inst. The bore 628 is configured to mate with a coupling memberof an inserter instrument, such as the coupling member of the inserterinstrument 30, to thereby couple the trial implant 522 to the inserterinstrument.

As shown in FIG. 9A, the second mating portion 214 defines a primaryarticulation interface, such as a superior articulating surface 632 andan auxiliary articulation interface, such as an engagement feature 636for coupling the inferior plate 530 to the superior plate 526. Thesuperior surface 632 is curved along the longitudinal direction and isconvex. The convex superior surface 632 corresponds to the concaveinferior surface 608 of the superior plate 526. As shown in FIG. 9A, theengagement feature 636 is defined in the superior surface 632 andincludes a slot 640 that extends into the superior surface 632 and alongthe superior surface 632 in the longitudinal direction. The engagementfeature 636 further includes an opening 644 at a proximal end of theslot 640. The opening 644 has a lateral width that is greater than thelateral width of the slot 640 and configured to receive the engagementfeature 584 of the superior plate 526. In particular the opening 644 hasa width that is capable of receiving the second member 596 of thesuperior plate's engagement feature 584. As shown in FIG. 9C, theengagement feature 636 of the inferior plate 530 further includes acavity 650 below the slot 640. The cavity 650 has a lateral width thatis approximately equal to the lateral width of the opening 644, andextends in the longitudinal direction. As shown , the cavity 650includes an upper concave surface 654 and a lower convex surface 658.The surfaces 654 and 658 have similar arcs as the curved inferiorsurface 580 and the curved superior surface 632 respectively. Therefore,the superior plate 526 can move relative to the inferior plate 530 alongthe arc defined by the superior and inferior surfaces 580, 632, while atthe same time remaining coupled to each other.

As shown in FIGS. 10A-10C, the inserter instrument may include a lockingblock having a locking mechanism configured to restrict movement of thesuperior plate 526 relative to the inferior plate 530. As shown, theinserter instrument may include a locking block 670 having body 674 anda locking mechanism 678 extending distally from the body 674. As shown,the locking mechanism includes an upper wedge 682 and two lower wedges686. The upper wedge 682 includes an angled bottom surface 690 thatextends up as it extends distally from the body 674. The wedge 682 isconfigured to be received by the recess 562 of the superior plate 526,while the angled bottom surface 690 is configured to smoothly engage theangled bottom surface 566 of the recess 562. As shown, the wedge 682 iscentrally located and has an upper surface 694 that is flush with anupper surface 698 of the body 674. The two lower wedges 686 each includean angled upper surface 702 that extend down as they extend distallyfrom the body 674. The lower wedges 686 are configured to engage a space706 defined between the superior plate 526 and the inferior plate 530.As shown, the lower wedges 686 are located on either side of the upperwedge 682 and include lower surfaces 712 that are flush with a lowersurface 716 of the body 674.

As shown in FIG. 10C, when the locking mechanism 678 engages the locking558 of the trial implant 522, the superior plate 526 is restricted frommoving relative to the inferior plate 530. As shown, to restrict themovement, the upper wedge 682 of the locking block 670 engages therecess 562 of the superior plate 526 and the lower wedges 686 engage thespace or gap 706 between the superior plate 526 and the inferior plate530 to thereby wedge the superior plate 526 between the upper wedge 682and the lower wedges 686 and restrict the superior plate's movement.

As shown in FIGS. 11A-11F, the trial implant may be configured to movein more that one direction. For example, as shown, a trial implant 800includes a superior plate 804 coupled to an inferior plate 808, suchthat the superior plate 804 is capable of moving in all directionsrelative to the inferior plate 808, as shown in FIGS. 11B and 11C.

As shown in FIGS. 11A and 11D, the superior plate 804 includes agenerally oval shaped body 812 having a first mating portion 816 coupledto a bottom or inferior side of the body 812. As shown, the body 812defines an upper or superior, or outer transverse engagement surface 822configured to contact the inferior endplate of the superior vertebralbody 10 a, and a bottom surface 826 configured to mate with the firstmating portion 816. The superior surface 822 includes a pair of spacedapart rails or grooves 834 disposed along the longitudinal direction forreceiving arms of a distractor instrument, such as the distractorinstrument 400 shown in FIG. 10.

As shown in FIG. 11D, the bottom surface 826 of the superior plate'sbody 812 defines a centralized recess 838. As shown, the recess 838 iscircular, though it should be understood that any shape may be used. Acenter portion 840 of the centralized recess 838 is deeper than aperiphery of the recess 838. Thus, the periphery of the recess defines aperipheral shoulder 842 that extends around the center portion 840 ofthe recess 838. Proximate to a center of the centralized recess 838 is abore 846 that extends transversely into the body 812.

As shown in FIGS. 11A and 11D, the first mating portion 816 is separatefrom the body 812 and is coupleable to the bottom surface 826 of thebody 812. The first mating portion 816 includes a circular protrusion850 that extends in an upward direction. As shown in FIG. 11D, thecircular protrusion 850 of the first mating portion 816 mates with thecenter portion of the circular recess 838 of the body 812, while theremainder of the first mating portion 816 mates with the shoulder 842 ofthe recess 838. The first mating portion 816 further defines a primaryarticulation interface, such as an inferior articulating surface 860 andan auxiliary articulation interface, such as an engagement feature 864for coupling the superior plate 804 to the inferior plate 808. Theinferior surface 860 is curved and forms a concave hemisphere. As shownin FIGS. 11A and 11D, the engagement feature 864 is a bore 870 thatextends into the inferior surface 580 and through a top side of theprotrusion 850. As shown, the bore 870 is disposed proximate to thecenter of the inferior surface 860 and aligns with the 846 that extendsinto the recess 838 of the superior plate body 812.

As shown in FIGS. 11A and 11D, the inferior plate 808, includes agenerally oval shaped body 880 having a second mating portion 884incorporated into a top or superior side of the body 880. As shown, thebody 880 defines a lower or inferior, or outer transverse engagementsurface 888 configured to contact the superior endplate of the inferiorvertebral body 10 b. The inferior surface 888 includes a pair of spacedapart rails or grooves 892 disposed along the longitudinal direction forreceiving lower arms of a distractor instrument, such as the lower armsof the distractor instrument 400 (shown in FIG. 10).

As shown in FIGS. 11A and 11D, the second mating portion 884 defines aprimary articulating interface, such as a superior articulating surface896 and an auxiliary articulating interface, such as an engagementfeature 900 for coupling the inferior plate 808 to the superior plate804. The superior surface 896 is curved and forms a convex hemisphere.The convex superior surface 896 corresponds to and mates with theconcave inferior surface 860 of the superior plate 804. As shown, thesecond mating portion 884 further includes a bore 904 that extendsthrough the superior surface 896 and into a cavity 908 defined withinthe second mating portion 884. The cavity 908 is circular and has adiameter that is greater than the diameter of the bore 904 that leadsinto the cavity 908. The second mating portion 884 further includes aplug 912 that is separate from the remainder of the second matingportion 884. As shown, the plug 912 includes a disc 916 and a pin 920that extends up from an upper surface of the disc 916. As shown in FIG.11D, the plug 912 is disposed within the cavity 908 of the second matingportion 884. In particular, the disc 916 of the plug 912 is placedwithin the cavity 908 while the pin 920 extends up through the bore 904of the second mating portion 884. As shown in FIG. 11D, the pin 920extends through the bore 904 of the second mating portion 884, throughthe bore 870 of the first mating portion 816 and into the bore 846 ofthe superior plate's body 812 to thereby couple the inferior plate 808to the superior plate 804. In this way, the cavity 908, the bore 904,and the plug 912 define the engagement feature 900 of the second matingportion 884.

As shown in FIGS. 11B, 11C, 11E, and 11F, the superior plate 804 isconfigured to move relative to the inferior plate 808. For example, thesuperior plate 804 may be moved to a first position as shown in FIGS.11B and 11E, in which the superior plate 804 is moved laterally to theleft about the inferior plate 808. In particular, the plug 912 rocks tothe left within the cavity 908 while the inferior surface 860 of thesuperior plate 804 slides to the left along the superior surface 896 ofthe inferior plate 808. As shown in FIGS. 11C and 11F, the superiorplate 804 may be moved to a second position, in which the superior plate804 is moved laterally to the right about the inferior plate 808. Inparticular, the plug 912 rocks to the right within the cavity 908 whilethe inferior surface 860 of the superior plate 804 slides to the rightalong the superior surface 896 of the inferior plate 808. Though notshown, the superior plate 804 may also be moved to a third position inwhich the superior plate 804 is moved distally about the inferior plate808, and to a fourth position in which the superior plate 804 is movedproximally about eh inferior plate 808. furthermore, the superior plate804 may be moved to additional positions between any of the first,second, third, and fourth positions. That is, the hemispherically curvedinferior and superior surfaces 860, 896, allow the superior plate 804 tomove along an arc in any direction relative to the inferior plate 808.

In another embodiment and in reference to FIGS. 12A and 12B, the trialimplant system 26 may include a trial implant 950 and an inserterinstrument 954 for inserting the trial implant 950 into anintervertebral space. The trial implant 950 is similar to the trialimplant 800 shown in FIGS. 11A-11F and is configured to have differentheights, while the inserter instrument 954 includes a protractor member958 configured to measure the required angle on the plates to fill thelordotic angle between the vertebral bodies.

As shown in FIG. 12B, the trial implant 950 includes a superior plate962 coupled to an inferior plate 966. As shown, the superior plate 962and the inferior plate 966 include corresponding primary articulatinginterfaces, such as hemispherical articulating surfaces 970, 974. Inparticular, the superior plate 962 includes a body 968 coupled to afirst mating portion 978 having a concave inferior surface 970, whilethe inferior plate 966 includes a body 980 coupled to a second matingportion 982 having a convex superior surface 974 configured to mate withthe inferior surface 970. As shown, the second mating portion 982 isseparable from inferior plate body 980. Therefore, the inferior plate966 may be fit with different second mating portions 982 havingdifferent heights to cover various disc heights.

As shown in FIG. 12B, the superior plate 962 and the inferior plate 966each include a coupling member such as a pair bores 990 extending into aproximal surface of each plate 962 and 966. The bores 990 are configuredto receive fixation elements, such as bolts 994 to thereby couple theinserter instrument 954 to the trial implant 950. The inferior plate 966further includes a square protrusion 998. that extends proximally fromits proximal surface.

As shown in FIGS. 12A and 12B, the inserter instrument 954 includes alower arm 1000, an upper arm 1004, and a measuring member, such as aprotractor member 958 extending between the lower arm 1000 and the upperarm 1004. As shown, the lower arm 1000 includes a lower arm body 1008that is elongate in the longitudinal direction and a coupling member1012 that extends distally from the body 1008. As shown, the couplingmember 1012 defines a recess 1016 and a pair of wings 1020 that extendlaterally out from the recess 1016. Each wing 1020 includes a bore 1024that extends through the wing 1020 in the longitudinal direction. Eachbore 1024 is configured to receive a bolt 994 to thereby couple thelower arm 1000 to the inferior plate 966. When the lower arm 1000 iscoupled to the inferior plate 966 the protrusion 998 is received by therecess 1016 defined by the lower arm's coupling member 1012. Similar tothe lower arm 1000, the upper arm 1004 includes an upper arm body 1028that is elongate in the longitudinal direction and a coupling member1032 that extends distally from the body 1028. As shown, the couplingmember 1032 includes a pair of bores 1036 that extend through thecoupling member 1032 in the longitudinal direction. Each bore 1036 isconfigured to receive a bolt 994 to thereby couple the upper arm 1004 tothe superior plate 964.

As shown in FIG. 12B, the upper arm 1004 further includes a transverseslot 1040 that extends through the upper arm body 1028 proximate to theproximal end of the arm body 1028. The protractor member 958 is rigidlycoupled to the lower arm 1000 and extends up toward the upper arm 1004and through the slot 1040 defined by the upper arm body 1028. Theprotractor member 958 is curved and includes indicia 1044 fordetermining the angle on the plates to fill the lordotic angle betweenthe vertebral bodies. Thus, the upper arm 1004 is capable of rotatingthrough an arc defined by the protractor body 958. Initially the upperarm 1004 should be rigidly coupled to the lower arm 1000 while the trialimplant 950 is being inserted into the intervertebral space. To lock theupper arm 1004 relative to the lower arm 1000, the inserter instrument954 further includes a lock screw 1050 configured to extend through alateral bore 1054 defined in the upper arm body 1028 and into a slot1058 defined by the protractor member 958.

In operation, the trial implant 950 is initially coupled to the inserterinstrument 954 such that the upper arm 1004 is rigidly coupled to thelower arm 1000. The trial implant 950 may be inserted into theintervertebral space by hammering a proximal end 1062 of the lower arm1000. Once properly inserted, the lock screw 1050 is released to allowthe upper arm 1004 to rotate. The angle between the upper arm 1004 andthe lower arm 1000 can be read from the indicia 1044 of the protractormember 958 to thereby determine the required angle on the plates to fillthe lordotic angle between the vertebral bodies.

In another embodiment and in reference to FIGS. 13A-13C, the trialimplant system 26 may include a trial implant 1100 and an inserterinstrument 1104 for inserting the trial implant 1100 into anintervertebral space. The trial implant 1100 and the inserter instrument1104 are configured to determine the proper angle of the plates.

As shown in FIG. 13C, the trial implant 1100 includes a superior plate1108 coupled to an inferior plate 1112. As shown, the superior plate1108 and the inferior plate 1112 include corresponding primaryarticulation interfaces, such as hemispherical articulating surfaces1116, 1120. In particular, the superior plate 1108 includes a body 1124coupled to a first mating portion 1128 having a concave inferior surface1116, while the inferior plate 1112 includes a body 1132 coupled to asecond mating portion 1136 having a convex superior surface 1120configured to mate with the inferior surface 1116.

As shown, the superior plate 1108 includes an elongate member 1140extending proximally from the body 1124. A shown, the elongate member1140 includes a dove tailed recess 1148 extending into a top surface ofthe elongate member 1140 and longitudinally through the proximal end ofthe elongate member 1140 and out the distal end of the body 1124. Theelongate member 1140 further includes a protrusion 1152 that extendsdown from a bottom surface of the member 1140. As shown in FIG. 13C, thesuperior plate 1108 further includes a protrusion 1156 that extendsproximally from a proximal surface of the elongate member 1140. Asshown, the protrusion 1156 defines a portion of a cylinder.

Like the superior plate 1108, the inferior plate 1112 includes anelongate member 1160 extending proximally from the body 1132. As shown,the elongate member 1160 includes a dove tailed recess 1164 extendinginto a bottom surface of the elongate member 1160 and longitudinallythrough the proximal end of the elongate member 1160 and out the distalend of the body 1132. The elongate member 1160 further includes a bore1172 extending into a top surface of the member 1160. As shown, the bore1172 is configured to receive the protrusion 1152 of the superior plate1108 to restrict longitudinal movement of the superior plate 1108relative to the inferior plate 1112. As shown in FIG. 13C, the inferiorplate 1112 further includes a protrusion 1176 that extends proximallyfrom a proximal surface of the elongate member 1160. As shown, theprotrusion 1176 defines a portion of a cylinder. When the superior plate1108 is mated with the inferior plate 1112, the protrusion 1156 of thesuperior plate 1108 and the protrusion 1176 of the inferior plate 1112mate to define a complete cylinder having external threads to therebydefine a coupling member of the trial implant 1100. As shown, however,the protrusion 1156 of the superior plate 1108 has a longitudinal lengththat is greater than the longitudinal length of the protrusion 1176 ofthe inferior plate 1112.

As shown in FIGS. 13A and 13B, the inserter instrument 1104 includes acylindrical body 1180 that is elongate in the longitudinal direction. Adistal end of the body 1180 defines a bore 1184 having internal threads.The bore 1184 is configured to receive the completed cylinder of thetrial implant 1100 to thereby couple the inserter instrument 1104 to thetrial implant 1100. The inserter instrument further includes a secondbody 1188 coupled to a proximal end of the body 1180 that is elongate inthe transverse direction. The second body member 1188 includes a pair ofslots 1192 that through the second body 1180 and along the body 1180 inthe transverse direction. As shown, the slots 1192 are open at theirrespective ends.

As shown in FIGS. 13A and 13B, the inserter instrument 1104 furtherincludes a pair of mono-chisels 1200. Each mono-chisel 1200 includes achisel body 1204 that is elongate in the longitudinal direction.Extending from a distal end of the chisel body 1204 is a chisel portion1208. Each chisel portion 1208 includes a dove tail 1212 extending alongits longitudinal length. The dove tails 1212 are configured to engagethe dove tailed recesses 1148, 1164 of the superior and inferior plates.Each chisel 1200 includes an edge 1220 on an opposite side of the chiselportion's dove tail 1212. As shown, each chisel 1200 extends through arespective slot 1192 of the second body member 1180. Thus, as thesuperior plate 1108 or the inferior plate 1112 rotate, the chisels 1200will slide within their respective slots 1192.

In operation, the trial implant 1100 is coupled to the inserterinstrument 1104, and then the trial implant 1100 is inserted into theintervertebral disc space. The body 1180 of the inserter instrument 1104is then unscrewed from the trial implant 1100 to release the superiorand inferior plates 1108, 1112. If the chosen angles are correct and thedisc removal is properly done, the superior and inferior plates 1108,1112 will not move, but if one of them is not correct (for the anglesare too small) the superior plate 1108 will rotate about thearticulating surface 1120 of the inferior plate 1112, showing the needfor a greater angle. In this case the trial implant 1100 should beremoved. To this end, the body 1180 of the inserter instrument 1104should be translated forward to initially grab the protrusion 1156 ofthe superior plate 1108. As the body 1180 is translated further forwardthe protrusion 1156 is pushed down until it mates with the protrusion1176 of the inferior plate 1112 to complete the cylindrical shape of thetrial implant's coupling member. By rotating the body 1180 the inserterinstrument 1104 will be reattached to the trial implant 1100. Now thetrial implant 1100 may be removed and the new one will be selected to beimplanted. This process may be repeated until the correct trial implanthas been selected. To achieve the correct angles on the superior andinferior plates 1108, 1112, the surgeon may start with lower angles andbuild up by truing higher angles until an optimum angle is achieved.Once the correct angles are determined the two chisels 1200 may be usedto perform keel cuts in the vertebral bodies. Because the chisels 1200are parallel to the superior and inferior plates 1108, 1112. During theprocedure the dove tailed recesses 1148, 1164 of the superior andinferior plates may be used in X-ray images as guides for determiningthe midline of the vertebral bodies.

It should be understood that any of the trial implants disclosed may besold as a kit including various sizes of the trial implants, as well asa kit of trial implants and permanent implants. Furthermore, any of thetrial implants may be sold as a kit with any of the inserter instrumentsincluding chisels that are disclosed.

It should also be understood that the disclosed trial implantsillustrate that trial implants usable in connection with any of thetrial implant systems described herein can be configured as to provide arange of numerous possible geometries and configurations. While thetrial implant systems of the present invention have been described inreference to surgical procedures for replacing a damaged intervertebraldisc with a total disc replacement implant, it is understood that theteachings of the present invention are easily configurable for surgicalprocedures for fusing a damaged disc space using an interbody spacer. Itshould also be appreciated by those skilled in the art that changescould be made to the embodiments described above without departing fromthe broad inventive concept thereof. Furthermore, it should beappreciated that the structure, features, and methods as described abovewith respect to any of the embodiments described herein can beincorporated into any of the other embodiments described herein unlessotherwise indicated. It is understood, therefore, that this invention isnot limited to the particular embodiments disclosed, but is intended tocover modifications within the spirit and scope of the presentdisclosure.

What is claimed:
 1. A method of determining optimal dimensions of apermanent articulating total disc replacement implant or staticinterbody spacer, the method comprising: coupling an inserter instrumentto a trial implant, the trial implant including a superior plate coupledto an inferior plate; temporarily restricting movement of the superiorplate relative to the inferior plate; inserting the trial implant intoan intervertebral space; unrestricting movement of the superior platerelative to the inferior plate; and determining the optimal dimensionsof the permanent articulating total disc replacement implant.